Single dopants in dopant-rich environment. (a) Device structure of a phosphorus-doped SOI-FET with the channel containing several donors. (b) SEM image of the channel area with an illustration of random donor arrangement. (c) An example of device characteristics with a single isolated first peak, indicating single-electron tunneling via a donor QD even in a donor-rich channel. (d) Zoom in on the first peak (inset: single-electron tunneling via a donor in a donor-rich channel).